1. Field of the Invention
This invention relates to a monitor for monitoring the situation of a broad area by means of a panoramic image obtained by shooting the surroundings, sequentially changing the shooting direction and also to a monitoring method, a computer program and a recording medium to be used with such a monitor.
This application claims priority of Japanese Patent Application No. 2003-415744, filed on Dec. 12, 2003, the entirety of which is incorporated by reference herein.
2. Description of Related Art
Electronic still cameras have been and being popularly used. They are adapted to convert light transmitted through a lens as a result of shooting a target by means of a solid state image pickup element such as CCD into image signals and record the image signals on a recording medium. They can also reproduce the recorded image signals. Many electronic still cameras are equipped with a monitor that can display a picked up still image so that a specific one of the recorded still images may be displayed there. In such an electronic still camera, the image signals supplied to the monitor correspond to an image of the target of shooting. Thus, it is an image of a very limited area that can be displayed at a time. In other words, it has not been possible to monitor the situation of a broad area.
In view of the above identified circumstances, monitoring cameras that can continuously shoot a target, sequentially shifting the shooting direction, to obtain a panoramic view of the target by arranging a plurality of unit images in order to monitor the situation of a broad area have become popular. Particularly, in recent years, techniques of reducing the size of each image and synthetically combining a plurality of images into a single image to produce video signals of a single frame have been proposed (see, inter alia, Patent Document 1: Jpn. Pat. Appln. Laid-Open Publication No. hei 10-108163). Additionally, central monitoring/recording systems adapted to monitor a broad area by collecting images that are obtained by means of a plurality of monitoring video cameras arranged at respective positions have also been proposed (see, inter alia, Patent Document 2: Jpn. Pat. Appln. Laid-Open Publication No. 2000-243062).
When shooting a target area with a predetermined view angle by means of a known monitoring camera as shown in FIG. 1 of the accompanying drawings, it is necessary to sequentially shift the shooting direction both horizontally and vertically. When, for example, the size of the target area is expressed by s×t times of the frame size of each image (to be referred to as unit image) obtained by shooting a small region of the target area from a given view angle, it is necessary to select at least s×t shooting directions.
To be more specific, the target is shot by aligning the shooting direction of the monitoring camera to coordinates (1, 1) of the upper left corner. Then, the shooting direction of the monitoring camera is shifted sequentially and horizontally to coordinates (2, 1), (3, 1), (4, 1), . . . , (s, 1) to shoot the target continuously. After completing the operation of shooting the first row, the target is shot by aligning the shooting direction of the monitoring camera to coordinates (1, 2) of the second row and then shifting the shooting direction sequentially and horizontally. After repeating the above operation until the shooting direction is aligned to coordinates (s, t) for shooting the target, the s×t unit images are put together to synthetically produce an image of the entire target area.
However, when a watchman tries to detect a change in the target area, using the monitored image recorded on a recording medium such as a video tape in a manner as described above, he has to observe every inch of the target area in the monitored image that is updated continuously by each scanning motion of the camera. Particularly, the watchman has to identify any minor change in the image and appearance of a small object at the cost of a large effort and time. Additionally, since such a monitoring system heavily relies on the eyes of the watchman, it inherently involves a risk that changes and appearances of objects can be overlooked.
Still additionally, when a change is detected in the target area, the watchman has to analyze the situation and the cause of the change in detail by referring to the image data recorded in the past to further raise the load on the part of the watchman.
Furthermore, in a system where any difference of luminance between panoramic images taken with time intervals calls watchman's attention and the target area is what is shown in FIG. 1, the road leading to the entrance of the church may frequently calls watchman's attention because many people may be walking there and hence movements may be detected also frequently. If the watchman needs to monitor small regions of the target area other than the road where many movements may be detected, he may be constantly annoyed by the movements on the road that may arise on the road because they inevitably call his attention. Then, the watchman can eventually mix up the changes detected on the road and those detected in other small regions of the target area so that he may not be able to reliably monitor the target area.